The introduction of time-fractional derivatives in the Navier-Stokes equations goes back to Lions and was recently extensively studied by many authors. When motivating such problems authors tend generally to motivate fractional models instead. In some papers (the ones of Zhou and Peng for example) say that such equations can model anomalous diffusion in fractal media. What I am looking for is some concrete situations where time-fractional Navier-Stokes equations is the good way to model the fluid flow.